The present invention relates to one-component room temperature vulcanizable silicone rubber compositions and more particularly the present invention relates to one-component room temperature vulcanizable silicone rubber compositions having an acyloxy functional silane as the cross-linking agent.
Room temperature vulcanizable (RTV) silicone rubber compositions are well known. Generally, there are two types of such RTV compositions; a one-component RTV system and a two-component RTV system. The two-component RTV systems generally comprise a base silanol terminated diorganopolysiloxane polymer to which there is added a filler and which is packaged in a separate package. There is then formed the second package of an alkyl silicate or partial hydrolysis product of an alkyl silicate as the cross-linking agent in combination with the metal salt of a carboxylic acid as the curing catalyst. The two packages are stored separately. When it is desired to cure the composition the two packages are mixed and applied to whatever form that is desired. Within a period of 24 hours the resulting mixture will cure to a silicone elastomer either in the presence or absence of moisture. Various types of ingredients can be added to this basic composition such as, self-bonding additives as disclosed in Lampe and Bessmer, U.S. Pat. No. 3,888,815. For instance, in the foregoing Lampe and Bessmer patent there is disclosed an amino functional silane which can be utilized as self-bonding additives for such two-component RTV systems.
There are also SiH-olefin platinum catalyzed room temperature vulcanizable silicone rubber compositions, however, such compositions are not pertinent to the present disclosure and as such will not be discussed in detail. With respect to the above two-component RTV systems these are to be distinguished from the one-component systems. Basically, such one-component RTV systems comprise a silanol-terminated diorganopolysiloxane base polymer to which is added a filler and various other ingredients. There is also added to this mixture of ingredients a functional silane as a cross-linking agent. The two most common cross-linking agents for such one-component RTV systems is an acyloxy functional silane as a cross-linking agent or an alkoxy functional silane as a cross-linking agent, examples of the two being methyltrimethoxy silane and methyltriacetoxy silane. To this cross-linking agent there is also added a metal salt of a carboxylic acid of a metal ranging from lead to manganese in the Periodic Table as the curing catalyst. The foregoing basic ingredients, that is, the silanol polymer, the filler, the functional silane and the metal salt of a carboxylic acid alone or with other additives, are mixed together in an anhydrous state to form a flowable mixture which is packaged as such. When it is desired to cure the composition the seal on the waterproof package is broken, the material is applied to whatever form that is desired and upon exposure to atmospheric moisture, it cures to a silicone elastomer. Examples of such one-package RTV systems are to be found in the following U.S. Pat. Nos.--Bruner, 3,035,016; Ceyzeriat 3,133,891; Nitzsche and Wick 3,065,194; Brown et al 3,161,614; Cooper 3,383,355; Matherly 3,499,859; Cooper et al 3,542,901; Brown et al 3,122,522; Brown et al 3,170,894; Weyenberg 3,175,993; Smith and Hamilton 3,689,454 and 3,779,986; Weyenberg 3,294,739 and 3,340,067; Clark et al 3,719,635; Beers 3,382,205, 3,779,986, 3,065,194, 2,294,739, 3,334,067 and 3,708,467.
The above are not all inclusive of all of the patents in the one-component RTV system, but give a representative description of some of the basic patents in the area. Recently, there issued a Beers, U.S. Pat. No. 4,100,129, which discloses a one-component RTV system having an alkoxy functional silane as a cross-linking agent, that is, methyltrimethoxy silane and a titanium chelate as the curing catalyst which composition is especially useful as a construction sealant. It should be noted herein that when such RTV compositions, specifically the one-component RTV compositions are made in low modulus, they are especially suited as construction sealants, that is, they can be utilized to glaze or seal crevices in window panes in the construction of buildings or homes for sealing purposes to seal the elements out with advantage.
Accordingly, one of the desired properties of a construction sealant in specifically a single dwelling construction sealant is that it be paintable. The reason for this is asthetics. If the silicone sealant is paintable then it can be painted over and will not detract from the asthetics of the home of the building. Such paintable silicone sealants are also desired for high rise construction buildings. However, it should be noted that up to this time silicone sealants have not generally been paintable. An example of a paintable silicone sealant is to be found in the disclosure of DuJack, U.S. Pat. No. 3,600,352, which is incorporated into the present case by reference. Basically, this disclosure discloses a paintable silicone sealant which is produced by intermixing a silanol-terminated polymer with a silicone resin composed of monofunctional units and tetrafunctional units in which there is utilized as a filler, asbestos. Although this sealant has many desirable properties since asbestos is not a desired filler for silicone compositions, it is not an advantageous paintable silicone construction sealant. It also contains a solvent additive which is undesirable for environmental and sealant shrinkage reasons.
Another paintable silicone construction sealant is that disclosed in Schultz, U.S. Pat. No. 3,836,502, which is incorporated into the present case by reference. This patent discloses a two-part RTV system having as the paintable sealant imparting additive, a silane which is obtained by reacting a mercaptosilane with nadic anhydride or nadic methyl anhydride. Although such a silicone RTV sealant is paintable, it is a two-part RTV sealant in one respect, and in the other respect it is not an advantageous composition since it requires the incorporation of the mercaptosilane which is an expensive intermediate. Accordingly, it is highly desirable to find a means for making one-component RTV systems paintable and specifically one-component RTV acyloxy functional RTV systems paintable. The foremost attempt up to the present time at this, is to be found in Clark et al, U.S. Pat. No. 3,957,714, which is incorporated into the present case by reference. Basically, this patent discloses a paintable one-component RTV construction sealant which is paintable and has a monoalkyltriacetoxysilane as the cross-linking agent, and has to use an acicular calcium carbonate as the filler and an organic solvent, that is, to apply the sealant in an organic solvent.
It should be noted that such a composition, while paintable has many disadvantages; the most basic of which is the fact that there is utilized an organic solvent which may cause pollution problems. In another respect, the evaporation of the organic solvent after the application of the sealant results in shrinkage of the sealant which may cause rupture of the sealant from the surfaces to which it has been applied. In another respect, the evaporation of the solvent may cause pollution problems. In a further respect, the evaporation of the solvent upon curing of the sealant and after application of the sealant to the surface desired, will cause the sealant to shrink upon curing. Accordingly, if the paint is applied while there is still some solvent in the sealant, the sealant will further shrink causing the paint that is present on the sealant to crack. However, it should be noted that such one-component system, such as that disclosed in the Clark et al patent above, is paintable.
It should also be noted that calcium carbonate is disclosed as a filler in two-component RTV compositions suitable for dental purposes. Also, calcium carbonate is disclosed as a second and additional filler in the one-component alkoxy functional RTV system of Beers, U.S. Pat. No. 4,100,129. However, it should be noted that when calcium carbonate is disclosed or utilized as a filler in one-component RTV compositions which utilize methyltriacetoxysilane as the cross-linking agent, such compositions become unflowable in the uncured state. One-component RTV compositions have to be flowable in the uncured state otherwise they will not flow out of the caulking tube or to the waterproof package in which they are packaged so that they can be applied to whatever use they are needed for. Accordingly, this may have been the reason why Clark et al, U.S. Pat. No. 3,957,714 teaches the use of a solvent. It should be noted that Clark et al specifies that certain concentrations of solvent are necessary for his composition to be paintable and that an acicular calcium carbonate has to be used in his composition. The disclosure of Beers, U.S. Pat. application, Ser. No. 919,544, filed on June 27, 1978, entitled "Curable Compositions and Process", now abandoned, should also be noted. This patent application discloses a one-component RTV system having as the cross-linking agent an acyloxy functional silane in which the acyloxy group has from 6 to 30 carbon atoms and is most preferably 2-ethylhexanoxy, in combination with a highly trifunctional fluid so as to result in a composition with improved oil resistance and heat resistance as well as low odor and low-corrosiveness. Accordingly, it was unexpected in view of the disclosure of Clark et al that a one-component RTV system could be formulated which is paintable having as the cross-linking agent an acyloxy functional silane in which the acyloxy group has from 6 to 30 carbon atoms.
Accordingly, it is one object of the present invention to provide for an acyloxy functional one-part or one-component RTV system which is paintable.
It is an additional object of the present invention to provide for a solventless one-component RTV system having an acyloxy functional silane as the cross-linking agent, which composition is paintable.
It is yet an additional object of the present invention to provide for a solventless paintable one-component RTV system having an acyloxy functional silane as the cross-linking agent which utilizes several types of calcium carbonate as the filler.
It is yet another object of the present invention to provide for a process for producing a solventless paintable one-component RTV system which utilizes an acyloxy functional silane as a cross-linking agent.
These and other objects of the present invention are accomplished by means of the disclosure set forth herein below.